This invention deals generally with off road vehicles and more specifically with an all wheel drive vehicle that has proportional distribution of load among its wheels.
Off road utility vehicles are becoming quite common for recreational and some occupational purposes. During some seasons of the year they are heavily advertised on television, and those commercials almost always show them taking sharp turns and cresting hills at high speeds. That is all very well for the camera, but it is not easily accomplished in the real world without careful design of the vehicle. If the suspension system of such an off road vehicle is not designed to accommodate to rough terrain, it is easy to end up with one or more wheels off the ground or with very light loading on some wheels. In such circumstances the steering control of the vehicle can be dramatically affected. In fact, even on level ground, the steering on some vehicles can be negatively affected by merely placing a heavy load in the cargo carrying area.
This problem has been essentially solved by a suspension structure disclosed in U.S. Pat. Nos. 6,629,699; 6,536,545; 6,557,661; and 6,601,665 by Hurlburt, who is also the inventor of the invention described herein. The suspension system includes a “bogey beam” which is a beam parallel to the axis of the vehicle. For a four wheeled vehicle the front axle is mounted on the forward end of the bogey beam and a suspension strut connects the rear end of the bogey beam to the frame. On a six wheel vehicle, instead of the suspension strut the middle axle is attached at the rear end of the bogey beam.
For both the four and six wheel versions, the primary place the bogey beam is attached to the vehicle frame is at a pivot assembly between the front and rear attachment points of the axles or the suspension strut. The action of the bogey beam is best described in regard to the six wheel version. The simplest pivot assembly is a rod with an axis transverse to the common longitudinal axis of the vehicle and the bogey beam, so the bogey beam therefore pivots on the pivot assembly only in the vertical plane. Thus, as the front wheels and axle move upward, the middle wheels and axle moves downward. This action causes the load transferred from the pivot assembly to the bogey beam to be shared between the front and middle axles in proportion to the spacing of each axle from the pivot assembly. Since a typical sharing of the load is to have nearly equal loads on the front and middle axles, the typical location of the pivot assembly is approximately midway between the front and middle axles.
With the bogey beam attached to the frame at only the pivot assembly, the load on the entire front end of the vehicle is shared proportionally by the front and middle axles. Furthermore, with the use of conventional lateral pivoting of the axles around the vehicle axis, the axles themselves distribute the load equally between their two wheels, and the load at the front end is therefore distributed among all four wheels. This arrangement virtually assures that no distribution of the load on the vehicle can lift or lighten the load on the front steering wheels to the detriment of control.
The system described above has been utilized and proven very effective, but it has only been used with front steering wheels that are not driven. No vehicles with bogey beams have had driven front wheels.
It would be very desirable to be able to use the bogey beam suspension system on an all wheel drive vehicle.